Evaluation, compression and application of vibrotactile data

Student thesis: Doctoral ThesisDoctor of Philosophy


With the rapid development of mobile network and smartphones, the audio-visual communication has achieved great success. The degree of immersion, however, is limited as physical interaction is not allowed. Introduction of vibrotactile data can significantly improve immersive experience of telecommunication and augment conventional multimedia. While acquisition, compression, display and quality evaluation of audio-visual data have been well developed over the past decades, the research on vibrotactile data has just started recently. 
The main objective of this thesis is to design quality assessment, data compression algorithms and applications for vibrotactile data. As quality assessment is required for evaluating the performance of a codec, we develop the vibrotactile quality assessment prior to designing the vibrotactile codec. This thesis first presents a subjective evaluation protocol dedicated to vibrotactile data. Based on this protocol, subjective experiments are conducted to evaluate the performance of two common objective metrics, i.e. signal-to-noise ratio (SNR) and structural similarity (SSIM), in the vibrotactile domain. The results demonstrate that both of them have high correlation with human vibrotactile perception, so that SNR and SSIM can be used to evaluate the quality of vibrotactile data. Considering a realistic scenario where distortion varies with time, we propose a hybrid objective metric that composites SNR and SSIM. Subjective tests show that the hybrid metric outperforms SNR and SSIM. 
Next, we propose a vibrotactile data compression algorithm in the spirit of Weber’s law. As humans are more sensitive to intensity change when the amplitude of vibrotactile data is low, we apply a companding function to the vibrotactile data. In this way, the quantisation step of high amplitude is larger than that of low amplitude. The curve of the companding function is optimised through a datadriven approach. Subjective experiments are conducted to assess the performance of the proposed vibrotactile codec in terms of human perceived quality. The results demonstrate that no degradation is perceived with a compression ratio of 75%. Furthermore, the latency is much shorter and the computational complexity is much lower than the state-of-the-art. 
Moreover, two vibrotactile coding methods to represent letters, numbers, symbols, etc. for the visually impaired are proposed. We utilise a vibrotactile display to deliver consecutive vibrational signals to the users and manipulate the frequency and duration of the vibrational signals to code different information. To assess the performance of the vibrotactile coding method, subjective tests are conducted. The results demonstrate that participants are able to learn the codes in about 6-8 hours and recognise words and symbols at an accuracy over 90%. More importantly, the cost of the vibrotactile display is significantly less than that of the commonly-used braille display.
Date of Award1 Jan 2020
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorMischa Dohler (Supervisor), Toktam Mahmoodi (Supervisor) & Hongbin Liu (Supervisor)

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